The invention relates to a fuse of a semiconductor device, and a method for fabricating the same.
If at least one memory cell of a memory array of a semiconductor device has a defect in the manufacturing of the semiconductor device, the whole device does not serve as a memory, so that the whole device is defective.
However, although there is a defect in one memory cell of the memory device, the whole device is regarded as being defective and discarded, thereby decreasing the device yield.
To overcome this problem, presently, the semiconductor device is designed with redundancy cells, so that a defective cell may be replaced with a redundancy cell, resulting in repair of the whole memory, and thereby improving yield.
In a repair method using a redundancy cell, each cell array comprises a redundancy word line that substitutes a normal word line and a redundancy bit line that substitutes a normal bit line, and when a defect is generated in a specific cell, the normal word line or the normal bit line is substituted with the redundancy word line or the redundancy bit line.
In the memory device, when a defective cell is found through a test after wafer processing, a circuit is comprised to substitute an address corresponding to the defective cell with an address corresponding to the redundancy cell.
As a result, when an address signal corresponding to the defective cell is inputted, data contained in the substituted redundancy cell corresponding to the defective cell is accessed.
Of the above-described repair methods, a widely used method is to burn a fuse with a laser beam and blow the fuse, thereby substituting the path of an address.
A general memory device comprises a fuse unit configured to substitute an address path by irradiating a laser to the fuse to blow the fuse. A wire disconnected by laser irradiation is referred to as a metal fuse, and the disconnected site and its surrounding region are referred to as a fuse box.
In the conventional art, a blowing process is performed while an oxide film remains on the fuse. However, the thickness of the residual oxide film is not uniform, so that the blowing of the fuse is not performed normally, thereby decreasing the yield of the device. Specifically, after introduction of the metal fuse, the reduction of the yield of the device has been increased over an admission range.
In order to solve the above problem, a bare fuse that does not comprise an oxide film over the fuse has been suggested.
FIGS. 1a to 1d are cross-sectional diagrams illustrating a conventional method for forming a bare fuse of a semiconductor device.
Referring to FIG. 1a, a first insulating film 105 is formed over a semiconductor substrate 100 including a lower structure.
A first barrier metal layer 110, a metal layer 115 and a second barrier metal layer 120 are sequentially formed over the first insulating film 105.
The first barrier metal layer 110 and the second barrier metal layer 120 comprise one selected from the group consisting of a titanium (Ti) film and a titanium nitride (TiN) film. The metal layer 109 comprises aluminum.
The second barrier metal layer 120, the metal layer 115 and the first barrier metal layer 110 are patterned to form a plurality of fuse patterns 125.
Referring to FIG. 1b, an oxide film 130 is formed over the fuse pattern 125 and the first insulating film 105, and a second insulating film 135 is formed over the fuse pattern 125 and the first insulating film 105.
A passivation layer 140 is formed over the second insulating film 135. The passivation layer 140 comprises one selected from the group consisting of an oxide film and a nitride film.
Referring to FIGS. 1c and 1d, the passivation layer 140 and the second insulating film 135 are etched by an etching process with a repair mask to form a fuse open region 150 that exposes the fuse pattern 125.
The top portion of the fuse pattern 125 is further etched so that the thickness of the fuse pattern 125 becomes thinner. The second barrier metal layer 120 is completely removed, and the top portion of the metal layer 115 is partially etched. When the thickness of the fuse pattern 125 is too thick, blowing is not normally performed. As a result, since the fuse pattern 125 is not suitable to be used as a fuse, the top portion of the fuse pattern 125 is etched so that the thickness may become thinner.
The first insulating film 105 is partially etched, and the first barrier metal layer 110 formed in the bottom portion of the fuse pattern 125 as shown in ‘A’ is completely open. The first barrier metal layer 110 is oxidized in a subsequent process to change its property. As a result, the resistance of the first barrier metal layer 110 becomes higher. However, when the resistance is increased, the fuse which is not cut is recognized as being cut in a reliability test. While the first barrier metal layer 110 is oxidized, the volume is expanded so that the metal layer 115 formed over the first barrier metal layer 110 becomes loose.